Pumps: How to Select the Right Pump Step-by-Step

This tutorial will take you step-by-step through the process of selecting the right pump for your irrigation system.  (You can apply the pump principles here to other water uses that aren’t irrigation with a little common sense.)  You may be installing a brand new irrigation system, need to replace the pump on an existing system, or need to enhance the performance of an existing system by adding a booster pump.  You might need to pump water from a well, a stream, or a pond.  Whatever the situation we will cover it here, but you will need to do a bit of reading.  That is the do-it-yourself way, if you don’t want to take the time to read it and learn how, you should stop here, and hire a local expert to come out to your property, do the research necessary, and select a pump for you.

NOTE: There is no “easy way” to select a pump.  If anyone tries to tell you what pump you need without establishing what your needed flow (GPM or l/m) and pressure (PSI or bars) is they are just guessing.  That’s like asking how many marbles it takes to fill a jar.  Without knowing how big the jar is, and how big the marbles are, all you can do is take a wild guess!



Now first let’s start by getting you around the huge beginner’s mistakes.

Warning- don’t make a major mistake!

There are 3 major errors people often make in regards to irrigation pumps. All of these are VERY expensive errors to fix. So let’s get you on the right track from the very beginning!

Plan First!

Do not buy a pump until you have determined your exact water needs for flow and pressure!  Many people every year lose lots of money because they bought a pump before they designed their irrigation system, then discovered it wasn’t the right type or size.   A pump must be sized for the exact pressure and flow requirements of your irrigation system.  Way too many people ask “what horsepower do I need?”  Newbie question!  Pumps aren’t selected by horsepower.  You need a pump that produces the correct amounts and ratios of water flow and water pressure.  So design your irrigation system first, purchase the pump second!

Pump Labels:

Many (most?) prepackaged off-the-shelf pumps have misleading performance labels. They aren’t exactly lying to you, they just aren’t being very clear.  Often a pump or the pump’s package will be labeled with something similar to “20 GPM, 55 PSI”. Or it may say “20 GPM, 127 feet of lift”. In most cases the word “or” should be added. What they mean is 20 GPM or 55 PSI. This is critical! There is a huge difference in performance between a pump that produces 20 GPM at 55 PSI, and a pump that produces 20 GPM or 55 PSI.  You may even see this misleading information stamped right onto the pump identification tag on the pump body!

Think about it in terms of a car. What if you are looking to buy a car and see one with the performance listed as “seats 5, goes 80 mph”?  So you buy the car, load it up with 4 buddies and quickly discover it won’t go over 20 MPH.  What gives?  Well what they meant was it carries 5 passengers OR goes 80 MPH.  They didn’t lie to you, they just didn’t really tell you the whole truth either.  The car goes 80 MPH with 1 passenger but with 5 passengers it won’t go more than 20 MPH.   See the difference?

All this will make much more sense after you have read this article, but for now you need to be aware of this mislabeling problem right up front.  Watch out for the wording on the pump labels!



So called “Irrigation Pumps”:

A number of websites and stores sell pumps that they call “irrigation pumps” or “sprinkler pumps.” These are typically small, inexpensive pumps designed to operate a single, small sprinkler head on the end of a garden hose.  They are not made for sprinkler systems with more than one sprinkler.

Typically pumps that are suitable for sprinkler systems are marketed under the label “high pressure pumps”.

OK, warnings complete, let’s get started!


Selecting a Pump – Overview

There are many types of pumps, and a few methods of selecting the proper pump.  To keep it simpler, let’s narrow down to what you need so you aren’t reading stuff unrelated to your needs.  Select the link below for the statement that best describes your pumping need:

  1. I Need a New Pump for a New Irrigation System.
  2. I Need a New Pump for an Existing Irrigation System.
  3. I Need a New Irrigation System that Uses My Existing Pump.
  4. Need to improve the performance of an Existing Irrigation System to create more pressure of a higher flow (I need a Booster Pump.)
  5. Need a pump for a Rain Barrel Irrigation System.


Looking for an Irrigation System that will Use Your Existing Pump?

The Irrigation Design Tutorial will take you through the process of determining how much flow and pressure your pump can produce, then you will design the irrigation system to match those parameters.

It won’t hurt to learn a bit more about pumps before you go to the irrigation design.  Go to  Types of Water Pumps.


Booster Pump to improve the performance of an Existing Irrigation System

As you remember from the first of this tutorial (back when you were still awake), booster pumps are used to increase the water pressure. Therefore the required booster pump pressure is simply the desired pressure minus the existing pressure. Just remember that for most pump brands the pressure must be expressed in feet of head, not PSI!

PSI x 2.31 = feet head
Feet head x 0.433 = PSI

 

Example: The existing pressure in the water company mainline you will use to supply water for your sprinkler system is 35 PSI static. Static pressure means the water pressure when measured with all water flows shut off; no faucets running, ice maker is off, no sprinklers on, nobody taking a shower (don’t turn off the water if someone is in the shower!!!), etc. To measure static water pressure just get a pressure gauge at the hardware store and attach it to a water outlet someplace reasonably close to the irrigation system. Make sure all other water outlets are turned off, then turn on the water to the gauge only. The gauge will show the static water pressure.




Where was I? Oh yeah, you have 35 PSI existing pressure. But let’s say your irrigation system needs 50 PSI to operate correctly. So you decide to add a booster pump to create more pressure. The pressure increase needed is 50 – 35 = 15 PSI. So you need a booster pump that produces 15 PSI of pressure at whatever flow rate the irrigation system requires. But wait, for most pumps the pressure needs to be expressed in feet head, not PSI! So convert PSI to feet head. 15 PSI * 2.31 = 35 feet head (round the result up to the next whole number.) That wasn’t difficult at all!

There are many companies that build and sell pre-packaged booster pump systems. These pump packages come with everything you need pre-assembled and ready to go. Typical assemblies include the pump, electrical controls, any needed control valves, a frame to hold everything and an enclosure to protect it. All you do is install it on a concrete pad, connect the pipes, and connect it to the power source. For most people this is the best way to buy a booster pump.

Now that you know what the process is, let’s move on and start learning about pumps.  First up there are lots of different types of pumps used for irrigation systems: centrifugal, submersible, turbine, jet, etc..  Let’s determine which is the best type for your irrigation system.  Go to  Types of Water Pumps.